I think the bolded is a bit of an overstatement.
Assuming 1. KC - Scheif - Volare is cast in stone we have one flawed but decent line - as long as Vivaldi is healthy.
2. If we were to get Sillinger to play with Perfetti we could play Niederreiter with them to potentially make a decent line. Or one of Lambert or Chibrikov could play on that line. Namestnikov is also an option to move up to that line, as is Barron.
Not sure that any of those would meet the threshold of your idea of a good line or not.
Funny thing is that McGroarty just might be ready to fill that opening.
If we were to get a direct replacement for Ehlers, say Necas, 3. we still only have 2/3 of a 2nd line. We don't have a C for that line yet, other than Names who is a placeholder.
1. A first line playing 20 minutes a night while losing their matchups is not a good line. It's not even a decent one - it's bad. Breaking up that line should result in an improvement by itself.
2. X-Perfetti-Niederreiter is probably the best shot we have of internally replacing Ehlers' impact without acquiring a direct replacement. That alone requires Arniel to rely on Perfetti as the 2C, to break up the third line and weaken it to a degree, and for Chevy to find someone to complement 91 and 62 on that line - preferably someone with some scoring threat. And even then, that severely weakens the third line, since Nino wouldn't be on it anymore.
The third line could be considered a good offensive line, since it dominates its xG share and puts up a decent amount of 5v5 points to boot, but it's less impressive when time on ice is taken into consideration. I think we're at a point where Nino needs to be promoted to support the top 6, and Lowry's line needs to have its minutes cut - along with the expectations to put up points. It can be a fantastic shutdown line, but the point production cannot be emphasised when the top 6 is in the shape it's in.
3. Whoever they choose for the 2C role is going to be a risk. The thing is, if you get rid of Ehlers, you're not going to be equipped to manage the situation if that risk materialises.